1. Field of the Invention
The present invention relates to a solid-state image sensing device driving method and a solid-state image sensing apparatus.
2. Description of the Related Art
Image sensing apparatuses equipped with CCD type solid-state image sensing devices, such as a digital still camera and a digital video camera, have come into wide use rapidly. In a CCD type solid-state image sensing device, a large number of photoelectric conversion devices are arranged in rows and columns perpendicular to the rows in one surface of a semiconductor substrate. Vertical charge transfer devices (VCCDs) each made of a CCD (charge coupled device) are arranged one by one, for example, along photoelectric conversion device columns each composed of a plurality of photoelectric conversion devices arranged in the column direction. A horizontal charge transfer device (HCCD) made of a CCD is disposed at respective output ends of the VCCDs.
In a single substrate type CCD type solid-state image sensing device for use in color image sensing, a color filter array is disposed on the large number of photoelectric conversion devices. This color filter array is constituted by color filters disposed one by one on the photoelectric conversion devices respectively. As for the kind of the color filter array, there are an RGB primary color filter array and a complementary color filter array. As for the complementary color filter array, there are known a color filter array composed of only complementary color filters and a color filter array composed of complementary color filters and green filters.
As for a solid-state image sensing device used as an area image sensor, there is known a solid-state image sensing device provided with a large number of photoelectric conversion devices arranged in the form of a tetragonal lattice. As for the color filter array widely used in such a solid-state image sensing device, there is a Bayer's array. The Bayer's array is an array in which rows each including R (red) filters and G (green) filters disposed alternately and repetitively and rows each including G filters and B (blue) filters disposed alternately and repetitively are disposed alternately and repetitively in the column direction. As for the photoelectric conversion device array, there is known a so-called honeycomb array in which odd-numbered rows of photoelectric conversion devices arranged in a row direction and even-numbered rows of photoelectric conversion devices arranged in the row direction are shifted from each other in the row direction by about a half of the arrangement pitch of the photoelectric conversion devices arranged in the row direction. In such a solid-state image sensing device, there is used a so-called G-striped R/B-fully-checkered array of color filters in which the row direction and the column direction in the Bayer's array are inclined at about 45°.
FIG. 5 is a view showing an operating condition of the HCCD when the solid-state image sensing device of the aforementioned honeycomb array is driven. In the example shown in FIG. 5, there is shown an operating condition when interlace drive for reading out charges is performed twice in such a manner that a first field and a second field are used. In the first field, charges are read out from photoelectric conversion device rows in each of which R photoelectric conversion devices for generating charges of an R component and B photoelectric conversion devices for generating charges of a B component are arranged alternately in a row direction. In the second field, charges are read out from photoelectric conversion device rows in each of which only G photoelectric conversion devices for generating charges of a G component are arranged in the row direction. Moreover, assume that an HCCD is two-phase driven.
First, in the first field, charges (hereinafter referred to as B charges) read out from the B photoelectric conversion devices and charges (hereinafter referred to as R charges) read out from the R photoelectric conversion devices are transferred to final stages of VCCDs and then transferred to the HCCD at time t=1. The charges transferred to the HCCD are transferred to adjacent parts of the HCCD at time t=2. Then, the transfer operation is repeated at times t=2, 3, 4, 5 . . . , so that a signal corresponding to the charges read out from one photoelectric conversion device row is output from an output amplifier. This operation is performed on all the photoelectric conversion device rows in each of which the R photoelectric conversion devices and the B photoelectric conversion devices are arranged alternately in the row direction. Thus, the first field is completed.
Next, in the second field, charges (hereinafter referred to as G charges) read out from the G photoelectric conversion devices are transferred to the final stages of the VCCDs and then transferred to the HCCD at time t=1. The charges transferred to the HCCD are transferred to adjacent parts of the HCCD at time t=2. Then, the transfer operation is repeated at times t=2, 3, . . . , so that a signal corresponding to the charges read out from one photoelectric conversion device row is output from the output amplifier. This operation is performed on all the photoelectric conversion device rows in each of which the G photoelectric conversion devices are arranged in the row direction. Thus, the second field is completed.
In this driving method, in the first field, charges of different color components are transferred to the HCCD in the row direction (horizontally) while mixed. For this reason, if the HCCD is poor in transfer efficiency, there occurs color mixing which is a phenomenon that R charges and B charges are mixed with each other due to transfer failure or the like to thereby result in deterioration of image quality (for example, a red subject forms an image close to magenta).
In order to avoid the color mixing, there has been proposed a method in which HCCDs are provided for the RGB photoelectric conversion devices respectively so that R, G, and B charges are transferred to the HCCDs separately. This method is however under the apprehension that the production cost will increase and lowering of image quality will be caused by variation in gain of an output amplifier connected to each HCCD.
In order to avoid the color mixing without provision of any special configuration, there has been therefore proposed a method for changing the transfer voltage of the HCCD or changing the driving frequency of the HCCD in accordance with image sensitivity (see JP-A-2004-304247) If the driving frequency of the HCCD is reduced in order to avoid color mixing as in the method disclosed in JP-A-2004-304247, it becomes difficult to satisfy increase in the number of photoelectric conversion devices.